As a defroster apparatus used for a pane, such as a front window and a rear window of a vehicle, a defroster apparatus locating a heating wire formed of a tungsten wire or the like all over the pane is known. In the conventional technique, by powering the heating wire provided all over the pane to raise a temperature of the pane by means of resistance heat, the pane is defogged or defrosted to ensure a field of view of a passenger.
In a defroster apparatus disclosed in JP2013-173402A, a tungsten wire is used as the heating wire. In this case, the heating wire has an increased cross-sectional area in order to prevent that electric resistance of the heating wire becomes too high because of a higher electric resistivity of tungsten. Thus, the heating wire using the tungsten wire is easily visible to an observer. The fact that the heating wire is visible to an observer such as a driver deteriorates a visibility of the observer through the pane.
There is recently known another defroster apparatus manufactured by creating a conductive pattern by photolithographic technique in place of a heating wire formed of a tungsten wire or the like. By powering the conductive pattern, a temperature of a pane is raised by means of resistance heat (JP2011-216378A and JP2012-151116A). This method is advantageous in that even a conductive pattern of a complicated shape can be easily formed. In JP2011-216378A and JP2012-151116A, a conductive pattern having an irregular shape obtained from a Voronoi diagram is formed, and the conductive pattern is used as a heating wire for raising a temperature of a pane.
FIG. 23 shows a partially enlarged conductive pattern 540 of a conventional defroster apparatus disclosed in JP2011-216378A and JP2012-151116A. In the conventional defroster apparatus, the conductive pattern 540 includes a plurality of connection elements 544 that extend between two branch points 542 to define opening areas 543. Each connection element 544 is formed of one straight line. The inventors of the present invention have conducted extensive studies on the defroster apparatus having such a connection element 544 and found that the conductive pattern 540 including the connection elements 544 may be visible to an observer (e.g., a passenger such as a driver), because of the shape of each connection element 544 formed of one straight line. When light such as outside light incident on the defroster apparatus enters a side surface formed of a flat surface of the connection element 544, the light incident on each position of the side surface is reflected on the side surface in substantially a certain direction. The reflected light is visible to an observer so that the conductive pattern 540 including the connection elements 544 is visible to the observer. The fact that the conductive pattern 540 including the connection elements 544 is visible to the observer such as a driver deteriorates a visibility of the observer through the pane.
The present invention has been made in view of the above circumstances. The first object of the present invention is to improve an invisibility of the conductive pattern of the defroster apparatus.
Various materials have been conventionally used for a heating wire of the defroster apparatus. For example, JP9-207718A discloses that a heating wire is made of tungsten. The heating wires disclosed in JP9-207718A are arranged in a so-called line and space pattern in which the plurality of heating wires are arranged in one direction.
The heating wire (thin conductive wire) in the defroster apparatus is desired to be as thin as possible, in order to improve a see-through property of a pane. However, the heating wire made of tungsten as in JP9-207718A has a relatively higher volume resistivity. Thus, in consideration of heat generation by the resistance heat of the electric wire upon being powered, it is difficult to make extremely thinner the heating wire. Thus, when the heating wire as disclosed in JP9-207718A is used in the defroster apparatus, there is a difficulty in exhibiting an excellent see-through property, while realizing a suitable heat generation function.
When the heating wires made of tungsten as disclosed in JP9-207718A are used in the defroster apparatus, the heating wires are sometimes heated/pressurized while being sandwiched between a pair of glass plates. In this case, before the heating/pressurizing step, the heating wires are generally manufactured as thin wires in a separate step. The heating wires formed in the separate step are placed and positioned in a desired pattern between a pair of glass plates, and the pair of glass plates in this condition are heated/pressurized. However, this positioning operation requires time and effort in order to precisely position the electric wires. In addition, when the pair of glass plates are heated/pressurized, there is a possibility that the electric wires are shifted from the determined positions.
The present invention has been made in view of the above circumstances. The second object of the present invention is to provide a heating plate and a method of manufacturing the same, which is capable of achieving an excellent see-through property because thin conductive wires disposed between glass plates are sufficiently thin, and of achieving an excellent heat generation upon being powered although the line widths of the thin conductive wires are thin, while a desired pattern of the thin conductive wires can be easily given to the heating plate with high precision.
In addition, the third object of the present invention is to provide a heating plate, a pattern sheet and a method of manufacturing the same, which is capable of achieving an excellent see-through property because the thin conductive wires disposed between glass plates are sufficiently thin, and of achieving an excellent heat generation upon being powered although the line widths of the thin conductive wires are thin.
JP2010-3667A discloses that heating wires are formed by exposing, developing and fixing a silver-salt photosensitive layer on a substrate. In addition, JP2010-3667A discloses that heating wires are formed by laminating a metal foil on a substrate and etching the metal foil, and that heating wires are formed by printing a paste containing metal particles on a substrate. Further, there is disclosed that heating wire are formed by printing heating wires on a substrate by means of a screen printing plate.
In such a defroster apparatus, a pair of glass plates, with a joint layer and heating wires being sandwiched therebetween, are heated and pressurized so as to manufacture a heating plate, and a defroster apparatus is formed of the heating plate. When such a heating plate is manufactured with the use of the heating wires disclosed in JP2010-3667A, the heating wires, which are integral with a sheet-like substrate, are disposed between a pair of glass plates, and then heated and pressurized. In more detail, a glass plate, a joint layer, a substrate integral with the heating wires, a joint layer and a glass plate are superposed in this order, and then heated and pressurized. In the thus manufactured heating plate, the one joint layer of the two joint layers is directly in contact with the glass plate and the substrate to join the glass plate and the substrate, and the other joint layer is directly in contact with the heating wire and the glass plate to join the heating wire and the glass plate.
Each heating wire disclosed in JP2010-3667A is formed to project along a normal direction of a sheet plane of a sheet-like substrate, and a sidewall thereof extends along the normal direction of the sheet pale of the substrate. The sidewall of such a heating wire may have an overhang shape, for some reason or other in the course of manufacture. The overhang shape means a shape of a heating wire that sidewall of the heating wire inclinedly extends to the outside in a direction along the sheet plane of the substrate, as a certain point in the sidewall moves away from the substrate along the normal direction of the sheet plane of the substrate. Such an overhang shape particularly tends to be formed when a heating wire is formed by etching or by printing a paste containing metal particles.
However, in the case where the sidewall of a heating wire has a shape that extends along the normal direction of the sheet plane of the substrate or the overhang shape, when the heating wire and the joint layer are brought into contact with each other in the heating and pressurizing step during the manufacture of a heating plate, it is difficult for the joint layer to get into a root side of the heating wire, so that bubbles are likely to remain around the sidewall of the heating wire. These bubbles may impair an appearance quality of the heating plate as well as resulting in glaring (glittering). Thus, in the manufacture of the heating plate, countermeasure against remaining of the bubbles is desired.
The present invention has been made in view of the above circumstances. The fourth object of the present invention is to restrain remaining of bubbles in a heating plate.